Fallback on critical failures

A fallback Task runs as a backup when a critical Task fails or is skipped. Its enabled reads any value that signals that — typically the critical Task’s .status, but a .result or a tag works just as well.

In the example, dashboard is the critical Task — it reads auth.result. If auth fails, dashboard is skipped. If dashboard itself fails, the result is the same: dashboard.status is not "done", so fallback runs. Reading .status instead of .result is what keeps fallback enabled — status is always available, even after a skip.

Uncomment the throw to see it:

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import { compose, createTask } from "@app-compose/core"

const auth = createTask({
  name: "auth",
  run: {
    fn: () => {
      // uncomment to make auth fail
      // console shows "fallback shown" instead of "dashboard ready"
      // 👇
      // throw new Error("[auth]: failed")
      return { id: 1 }
    },
  },
})

// critical to the app
const dashboard = createTask({
  name: "dashboard",
  run: {
    context: auth.result,
    fn: (user) => console.log(`#${user.id} dashboard is ready`),
  },
})

// runs when dashboard doesn't reach "done"
const fallback = createTask({
  name: "fallback",
  run: { fn: () => console.log("fallback shown") },
  enabled: {
    context: dashboard.status,
    fn: (status) => status !== "done",
  },
})

compose()
  .step(auth)
  .step(dashboard)
  .step(fallback)
  .run()

For shorter enabled blocks, when from @app-compose/coda returns the { context, fn: Boolean } pair in a single call.